1. Field of the Invention
The present invention relates to a radiation image capturing system and a radiation image capturing apparatus. Specifically, the present invention relates to a radiation image capturing apparatus which can detect start of irradiation of radiation and a radiation image capturing system which uses such apparatus.
2. Description of Related Art
Various radiation image capturing apparatuses are being developed. For example, there is a direct-type radiation image capturing apparatus which generates electric charge in a detecting element according to the amount of irradiated radiation such as X-ray, etc., to convert the electric charge to an electric signal. There is also an indirect-type radiation image capturing apparatus which converts the irradiated radiation to an electromagnetic wave with another wavelength such as visible light, etc., with a scintillator, etc., and then generates electric charge by a photoelectric conversion element such as photodiode, etc. according to energy of the converted and irradiated electromagnetic wave to convert the electric charge to an electric signal (in other words, image data). In the present invention, the detecting element in the direct-type radiation image capturing apparatus and the photoelectric conversion element in the indirect-type radiation image capturing apparatus are collectively referred to as a radiation detecting element.
Such type of radiation image capturing apparatus is known as an FPD (Flat Panel Detector). Conventionally, the radiation image capturing apparatuses were dedicated type apparatuses (also referred to as fixed type) formed together with a supporting stage, etc. (for example, see Japanese Patent Application Laid-Open Publication No. H9-73144). Lately, portable type (also referred to as cassette type) radiation image capturing apparatuses are developed and used where the radiation detecting element, etc., is stored in a housing so that the apparatus can be carried (for example, see Japanese Patent Application Laid-Open Publication No. 2006-058124, Japanese Patent Application Laid-Open Publication No. H6-342099).
For example, as shown in later described FIG. 3, FIG. 4, etc., in such radiation image capturing apparatuses, usually, a plurality of radiation detecting elements 7 are arranged two-dimensionally (matrix shape) on a detecting section P, and a switch element formed with a thin film transistor (hereinafter referred to as TFT) 8 is connected to each radiation detecting element 7. Usually, radiation image capturing is performed by irradiating radiation from a radiation generating apparatus 55 (see later described FIG. 5) to the radiation image capturing apparatus in a state with a predetermined capturing site (in other words, chest portion front view, lumbar spine side view, etc.) of a body, etc. of a subject in between.
Here, an off voltage is applied to each line L1 to Lx of a scanning line 5 from a gate driver 15b of a scanning driving unit 15 of the radiation image capturing apparatus to set all TFT 8 to an off state (later described electric charge accumulating state). In this state, when radiation is irradiated, electric charge is generated in each radiation detecting element 7 by irradiating the radiation, and the electric charge is accurately accumulated in each radiation detecting element 7. Then, after radiation image capturing, an on voltage is sequentially applied to each line L1 to Lx of the scanning line 5 from the gate driver 15b, and each TFT 8 is sequentially set to an on state. In this state, the electric charge generated and accumulated in each radiation detecting element 7 by irradiating radiation is sequentially discharged to each signal line 6, and each readout circuit 17 performs readout processing of image data D to read out the electric charge as image data D.
As described above, in order to accurately perform radiation image capturing, it is necessary to suitably apply off voltage to each line L1 to Lx of the scanning line 5 from the gate driver 15b to set each TFT 8 which are switch elements to the off state when the radiation is irradiated to the radiation image capturing apparatus. For example, in most conventional dedicated type radiation image capturing apparatuses, an interface is constructed with the radiation generating device. Signals are transmitted and received between each other to confirm that the radiation image capturing apparatus applied off voltage to each line L1 to Lx of the scanning line 5 and that the apparatus is set to the electric charge accumulating state. Then, the radiation is irradiated from the radiation generating apparatus.
However, for example, when the manufacturer of the radiation image capturing apparatus and the radiation generating apparatus are different, it is not always easy to construct an interface between each other, or it may not be possible to construct an interface. When an interface cannot be constructed between the radiation image capturing apparatus and the radiation generating apparatus, the radiation image capturing apparatus cannot know the timing that the radiation is irradiated from the radiation generating apparatus. Therefore, the radiation image capturing apparatus itself needs to detect that the radiation is irradiated from the radiation generating apparatus.
Lately, various radiation image capturing apparatuses are developed so that the radiation image capturing apparatus itself is able to detect the irradiation of radiation without depending on the interface between the radiation image capturing apparatus and the radiation generating apparatus. For example, Japanese Patent Application Laid-Open Publication No. 2010-104398 describes a radiation image capturing apparatus includes a radiation sensor (in other words, a sensor such as a module which is different from the radiation detecting element) and the radiation sensor detects the irradiated radiation to detect that the radiation is irradiated to the radiation image capturing apparatus. Moreover, for example, the pamphlet of WO 2011/135917 describes, before irradiating the radiation to the radiation image capturing apparatus, all TFT 8 (see later described FIG. 4, etc.) are set to an off state, the readout circuit 17 performs readout operation to perform readout processing of leak data dleak, and the apparatus itself is able to detect start of irradiation of radiation based on the read out leak data dleak. Further, for example, the pamphlet of WO 2011/152093 describes, before irradiating the radiation to the radiation image capturing apparatus, the scanning driving unit 15 and the readout circuit 17 are operated similar to the readout processing of image data D of the main image to perform readout processing of the image data, and the apparatus itself detects the start of irradiation of radiation based on the read out image data.
Below, the image data read out in the method of detecting the start of irradiation of radiation as described in the pamphlet of WO 2011/152093 is called irradiation start detecting data d, in order to distinguish such data from the image data D read out later as the main image. The method of detecting start of irradiation of radiation as described in the pamphlets of WO 2011/135917 and WO 2011/1592093 is described later (see later described detecting method 2A, 2B).
When the start of irradiation of radiation is detected based on the read out leak data dleak or the irradiation start detecting data d as described in the pamphlets of WO 2011/135917 or WO 2011/152093, as described later, there is a highly advantageous practical merit that it is possible to accurately detect start of irradiation of radiation under any capturing condition to perform capturing, for example, the radiation image capturing apparatus itself can accurately detect the start of irradiation of radiation even when weak radiation is irradiated to the radiation image capturing apparatus.
However, according to the method of detecting start of irradiation of radiation as described in the pamphlets of WO 2011/135917 and WO 2011/152093, the readout circuit 17 (see later described FIG. 4) needs to read out the leak data dleak. However, at present, the readout circuit 17 usually consumes a relatively large amount of electric power to read out data. Therefore, when such detecting methods are employed, there is a problem that the amount of electric power that is consumed becomes large when the detecting processing of start of irradiation of radiation is performed. Although such problem also occurs in a dedicated type radiation image capturing apparatus, especially when the amount of electric power that is consumed becomes large in the radiation image capturing apparatus which is a portable apparatus including a battery, the battery needs to be charged frequently and the number of radiation images which can be captured by one charge of the battery decreases. This causes problems such as reduction of efficiency in use of the radiation image capturing apparatus.
As described above, when the method of detecting start of irradiation of radiation as described in the pamphlets of WO 2011/135917 and WO 2011/152093 is employed, although it is possible to achieve the highly advantageous merit of being able to accurately detect start of irradiation of radiation under any capturing condition to perform capturing, there is a problem that the amount of electric power that is consumed becomes large.